Change the method of IntList equals from toString to ListEquality.equals. In my case, codegen 15x faster

[qpalwo]

I have a 6000-line proto file, and it takes one minute to generate Dart code using the Dart proto plugin. After changing to the ListEquality.equals method, it only takes 4.6 seconds. If I completely remove the commentBlock call and compile it into an AOT (Ahead-of-Time) artifact, it only takes 200ms.

❯ time protoc --dart_out=./dart/lib1 test.proto
protoc --dart_out=./dart/lib1 test.proto 62.60s user 0.75s system 100% cpu 1:03.31 total
❯ time protoc --dart_out=./dart/lib1 --plugin=protobuf.dart/protoc_plugin/bin/protoc-gen-dart test.proto
protoc --dart_out=./dart/lib1 test.proto 4.61s user 0.32s system 125% cpu 3.918 total

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